Infrared camera tube

ABSTRACT

An infrared camera tube which has a cathode, cathode aperture, focusing lens aperture, photoconductor and obscuring flap. The obscuring flap is located between the cathode and the photoconductor so as to block the undesirable infrared radiation therebetween.

United States atent 1 1 1 1 3,898,497

Saum et a]. Aug. 5, 1975 [54] INFRARED CAMERA TUBE 2,967,961 1/1961Heil 1. 315/10 X 3,324,327 6/1967 KOdam 313/101 X [75] Inventors: GeorgeA. Saum, F1or1ssant, M0,; 33,76,465 4/1968 Corpew v I i H 313/10 Hansslppach, Syracuse, 3,444,375 5/1969 Seamans, Jr. 250/833 IR AssigneezThe United States of America as 3,588,570 6/1971 OKeeffe 313/101 Xrepresented by the Secretary of the Air Force, Washington, DC. PrimaryExaminer-Maynard R. Wilbur Assistant E.\aminerS. C. Buczinski 7 Ffled'1970 Attorney, Agent, or Firm-Joseph E. Rusz; Jacob N. [21] Appl. No.177,357 Erlich [52] US. Cl. 313/388; 250/338; 2532/3/55}; ABSTRACT [51]Int. Cl. H01j31/49 An infrared camera tube which has a cathode, cath-[58] Field of Search 250/3 ode aperture, focusing lens aperture,photoconductor 313/1 11 and obscuring flap. The obscuring flap islocated between the cathode and the photoconductor so as to [56]Reference Cited block the undesirable infrared radiation therebetween.

UNITED STATES PATENTS 2 2,928,971 3/1960 Redington et a1. 313/80 x 1Clam" Drawmg F'gures BESBASY I WENTORs i 3 2 NM PATENTEDAUB 5W5 INFRAREDCAMERA TUBE BACKGROUND OF THE INVENTION This invention relates generallyto infrared camera tubes and, more particularly, to an infrared cameratube in which the infrared radiation from a hot thermionic cathode isprevented from reaching the photoconductor.

In conventional vidicon-type camera tubes, a cathode electrode isutilized to generate an electron beam that is focused on the area ofa'photoconducting element or target upon which a scene is imaged. Theheated cathode electrode (near 1,000K) produces infrared rays along withthe electron beamfThese infrared rays, although incident upon thetarget, do not afries. The infrared radiation, however, does travel in asubstantially straight line.

In the infrared camera tube of the instant invention a small flap,preferably of a good heat insulating material, is suspended in front ofthe cathode of the infrared camera tube. The diameter of the flap is ofsuch a size as to block out the infrared radiation, yet allow for theflow of electrons to pass around it. An electrical lens is 1 thenutilized to refocus the electron beam onto the infrared photoconductor.It is the instant invention which prevents the undesirable affect ofhaving infrared radiv ation pass to the photoconductor, and does so witha feet the output signal because the target of the conventional cameratube is insensitive to these rays. j

The infrared detecting system makes use of the fact that all physicalobjects emit infrared radiation. The amount and kind of radiationdepends upon the temperature of the object and its emissivity. Thus,when the objects are viewed by an appropriate infrared detecting system,any object at a different effective temperature stands out from itssurroundings. Since the thermionic cathode electrode in infrared cameratubes operate near 1000K considerable infrared radiation is generated.This radiation shines through the aperture in an electron gun, down thetube axis, and onto the infrared photoconductor. Unlike the target inthe conventional camera tubes, the target of an infrared camera tube issensitive to infrared rays. Thus, an undesirable photoconduction takesplace in the central portion of the photoconductor or target. Thisreduces the sensitivity of the center of the photoconductor and producesa troublesome white area in the center of the picture.

Many methods have been attempted in the elimination of these undesirableinfrared rays. For example, the R. W. Redington et al U.S. Pat. No.2,928,97l dated Mar. 15, 1960 and the Saum et al U.S. Pat. No. 2,947,896dated Aug. 2, 1960 by one of the inventors of this application, disclosecomplex procedures for eliminating these infrared rays. In fact, othersystems such as cool tunnel emitters and field emitter points have alsobeen utilized in trying to present a simple and effective way ofremoving the infrared rays. To date, however, these systems althoughsomewhat effective usually prove to be extremely expensive and complexin construction. Heretofore, there has yet to be devised a system ofremoving infrared rays in an infrared camera tube which is both highlyreliable and extremely simple in operation.

SUMMARY OF THE INVENTION The instant invention sets forth a system ofeliminating infrared rays in an infrared camera tube which overcomes allthe problems set forth hereinabove.

A conventional infrared camera tube has a hot cathode electrode whichproduces an electron beam to be utilized in conjunction with an infraredsensitive photoconductor. The cathode also generates a considerableamount of infrared radiation which in the case of an infrared cameratube is highly undesirable. In order to prevent the infrared radiationfrom reaching the photoconductor the infrared camera tube of thisinvention utilizes the fact that the electrons do not travel in exactstraight lines, but travel in somewhat curved trajectominimum of parts.

It is therefore an object of this invention to provide an infraredcamera tube which has an obscuring flap therein to block infraredradiation from reaching the photoconductor.

lt'isanother' object of this invention to provide a system' to blockinfrared radiation in an infrared camera tube which is economical toproduce and which utilizes conventional, currently available componentsthat lend themselves to standard, mass-producing manufacturingtechniques.

For a better understanding of the present invention together with otherand further objects thereof, reference is made to the followingdescription taken in connection with the accompanying drawing and itsscope will be pointed out in the appended claims.

DESCRIPTION OF THE DRAWING FIG. 1 is a schematic drawing of the infraredcamera tube of this invention with the obscuring flap out of position;and

FIG. 2 is a schematic drawing of the infrared camera tube of thisinvention with the obscuring flap in position.

DETAILED DESCRIPTION OF THE EMBODIMENT Reference is now made to FIG. 1of the drawing which shows the infrared camera tube 10 of this inventionwith the obscuring flap 12 (FIG. 2) out of position. The infrared cameratube 10 is made up of a conventional cathode electrode 14 and aninfrared sensitive photoconductor 16. The photoconductor 16 has a layerof any photoconductive material, such as germanium or silicon. suitablydoped with impurities, that is coated on the rear with a conductor film.The number of electrons from the beam 18 emanating from cathode 14 whichpasses through the photoconductive material at any point onphotoconductor I6 depends upon the amount of infrared radiation at thatpoint. Therefore, as shown in FIG. 1, any infrared radiation 20 alsoemanating from cathode 14 which passes to photoconductor 16 is highlyundesirable.

As shown in FIG. 2, the infrared camera tube 10 of this invention isfurther made up of an electron gun aperture or cathode aperture 22located adjacent cathode l4 and a focus lens aperture 24 locatedproximate phovtoconductor 16. An obscuring flap 12 made of any suitablenon-magnetic material, such as Stainless Steel 305 or Titanium which hasundergone an outgassing process is located within camera tube 10 at apoint 26 where the electrons begin to curve or bulge. The obscuring flap12 is of a diameter at least as great as gun aperture 22 but not sogreat as the diameter of the bulge. The specific size of the obscuringflap 12 allows for the infrared radiation 20 to be blocked but permitsthe electrons 18 to pass to photoconductor 16. The flap 12 may bemounted within camera tube by any conventional mounting arrangement 28.Focus lens aperture 24 redirects the electron beam 18 to photoconductorl6.

MODE OF OPERATION Referring again to FIG. 2, in operation the obscuringflap 12 is positioned within camera tube 10 at the area 26 of theenlarged electron beam 18. Upon actuation of the cathode 14, anyinfrared radiation 20 is blocked by the obscuring flap 12 while theelectron flow 18 upon being refocused by lens aperture 24 passes on tophotoconductor l6. Thereafter the infrared camera tube 10 of thisinvention functions as any ordinary infrared camera tube.

Although the invention has been described with reference to a particularembodiment, it will be understood to those skilled in the art that thisinvention is also capable of a variety of alternate embodiments withinthe spirit and scope of the appended claims.

We claim:

1. In an infrared camera tube having a cathode for producing an electronbeam and a photoconductor the improvement therein comprising a cathodeaperture of predetermined diameter located coincidental with the axis ofsaid cathode, an electrical focus lens located proximate saidphotoconductor for refocusing said electron beam, an obscuring flap ofheat insulating, nonmagnetic material located intermediate said cathodeaperture and said focus lens at a point where said electron beam beginsto bulge, said obscuring flap having a diameter at least as great assaid predetermined diameter but not so great as the diameter of saidbulge whereby an infrared radiation emanating from said cathode isblocked by said obscuring flap and the electrons pass to saidphotoconductor. 1:

1. In an infrared camera tube having a cathode for producing an electronbeam and a photoconductor the improvement therein comprising a cathodeaperture of predetermined diameter located coincidental with the axis ofsaid cathode, an electrical focus lens located proximate saidphotoconductor for refocusing said electron beam, an obscuring flap ofheat insulating, nonmagnetic material located intermediate said cathodeaperture and said focus lens at a point where said electron beam beginsto bulge, said obscuring flap having a diameter at least as great assaid predetermined diameter but not so great as the diameter of saidbulge whereby an infrared radiation emanating from said cathode isblocked by said obscuring flap and the electrons pass to saidphotoconductor.